Clean up E0740 explanation

GuillaumeGomez · GuillaumeGomez · commit 759de11f534b · 2020-07-29T14:06:29.000+02:00
diff --git a/src/librustc_error_codes/error_codes/E0740.md b/src/librustc_error_codes/error_codes/E0740.md
@@ -1,4 +1,4 @@
-A `union` cannot have fields with destructors.
+A `union` was declared with fields with destructors.
 
 Erroneous code example:
 
@@ -14,3 +14,5 @@ impl Drop for A {
     fn drop(&mut self) { println!("A"); }
 }
 ```
+
+A `union` cannot have fields with destructors.

Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,4 @@`
`1`		-A `union` cannot have fields with destructors.
	`1`	+A `union` was declared with fields with destructors.
`2`	`2`
`3`	`3`	`Erroneous code example:`
`4`	`4`
`@@ -14,3 +14,5 @@ impl Drop for A {`
`14`	`14`	`fn drop(&mut self) { println!("A"); }`
`15`	`15`	`}`
`16`	`16`	```
	`17`	`+`
	`18`	+A `union` cannot have fields with destructors.